Combination starter-generator

ABSTRACT

A combination starter-generator system for use in a vehicle is provided. The vehicle has an internal combustion engine and a battery. The system includes a starter-generator electrically coupled to the battery to generate a current and to start the internal combustion engine. A drive mechanism connects the starter-generator machine and the internal combustion engine. The starter-generator machine generates the current by receiving a charging torque from one side of the drive mechanism and starts the internal combustion engine by imparting a starting torque to a different side of the drive mechanism. The charging torque or the starting torque is a greater torque. A passive tensioning system cooperates with the drive mechanism to tension the drive mechanism only at the side of the greater torque.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is related to provisional application serial No.60/273,191 filed on Mar. 2, 2001 and bearing Attorney Docket No. DP-302111, the contents of which are incorporated herein.

TECHNICAL FIELD

[0002] This application relates generally to vehicles having acombination starter-generator. More specifically, this applicationrelates to tensioning systems and drives for combinationstarter-generators.

BACKGROUND

[0003] Prior internal combustion engine includes both a starter machineand a generator or alternator machine (hereinafter generator). Thestarter provides an engine-cranking torque to the flywheel or crankshaftof the engine in order to rotate the camshaft and facilitate themovement of the pistons during the ignition of the engine. The generatorprovides an electrical output in order to meet the electrical loads ofthe vehicle, as well as to charge the vehicle's battery. Generally, atorque is applied to a pulley of the generator by a belt frictionallyengaged with a pulley of the generator and a pulley of the engine inorder to generate the electrical charge from the generator.

[0004] The concept of using only one machine to do both functions,namely starting and generating, adds efficiency. Thus,starter-generators use less space, weigh less, eliminate the cost of oneof the machines and reduce assembly time. However, starter-generatorsgive rise to issues described below that affect the cost, complexity,and reliability of such starter-generator systems. Accordingly, there isa continuing need for inexpensive, reliable tensioning systems forstarter-generators.

SUMMARY

[0005] A combination starter-generator system for use in a vehiclehaving an internal combustion engine is provided. A drive mechanismconnects the starter-generator machine and the internal combustionengine. The starter-generator machine generates a current by receiving acharging torque from one side of the drive mechanism and starts theinternal combustion engine by imparting a starting torque to a differentside of the drive mechanism. Depending on the application, the chargingtorque or the starting torque is a greater torque. A passive tensioningsystem cooperates with the drive mechanism to tension the drivemechanism only at the side of the greater torque.

[0006] An apparatus for starting an internal combustion engine having astarter-generator machine is provided. The starter-generator machine isoperable in a first direction for generating a current and a seconddirection for starting the internal combustion engine. A drive mechanismconnects the starter-generator machine and the internal combustionengine by a non-adjusting gear ratio in a range between 2:1 to 3:1. Thestarter-generator machine operates in the first direction to generate acurrent by receiving a charging torque from the internal combustionengine imparted to a first side of the drive mechanism. Thestarter-generator machine operates in the second direction to start theinternal combustion engine by imparting a starting torque to a secondside of the drive mechanism. A first tensioning system cooperates withthe drive mechanism to tension the drive mechanism at the first sideduring application of the charging torque. A second tensioning systemcooperates with the drive mechanism to tension the drive mechanism atthe second side during application of the starting torque.

[0007] An active tensioning system for use on a drive mechanism isprovided. The drive mechanism creates a first slack side and a firsttight side of the drive mechanism. The drive mechanism also creates asecond slack side and a second slack side of the drive mechanism. Thefirst slack side and the second tight side are coincident. Similarly,the second slack side and the first tight side are coincident. Theactive tensioning system has a guide. A first idler sprocket isoperatively coupled with the first slack side of the drive mechanism andis slidable on the guide. A second idler sprocket is operatively coupledwith the second slack side of the drive mechanism and is also slidableon the guide. A spring connects the first idler sprocket and the secondidler sprocket. The spring also biases the first idler sprocket and thesecond idler sprocket towards one another such that upon creation of thefirst slack side and the first tight side, the first tight side actsupon the second idler sprocket to slide the first idler sprocket and thesecond idler sprocket upon the guide to tension the drive mechanism, andsuch that upon creation of the second slack side and the second tightside, the second tight side acts upon the first idler sprocket to slidethe first idler sprocket and the second idler sprocket upon the guide totension the drive mechanism.

[0008] A combination starter-generator system is provided. The vehiclehas an internal combustion engine and a starter-generator machine forgenerating a current and starting the internal combustion engine. Adrive mechanism connects the starter-generator machine and the internalcombustion engine. The starter-generator machine charges the battery byreceiving a charging torque from a first side of the drive mechanism.The starter-generator machine starts the internal combustion engine byimparting a starting torque to a second side of the drive mechanism. Thedrive mechanism compensates for differences in the charging torque andthe starting torque with a non-adjusting gear ratio in a range between2:1 to 3:1. An active tensioning system cooperating with the drivemechanism to tension the drive mechanism at the first side duringapplication of the charging torque or at the second side duringapplication of the starting torque.

[0009] The above-described and other features and advantages of thepresent invention will be appreciated and understood by those skilled inthe art from the following detailed description, drawings, and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a front view of a belt or chain drive mechanism;

[0011]FIG. 2 is a block diagram of a starter-generator circuit;

[0012]FIG. 3 is a first step of a control sequence of the circuit ofFIG. 2;

[0013]FIG. 4 is a second step of a control sequence of the circuit ofFIG. 2;

[0014]FIG. 5 is a third step of a control sequence of the circuit ofFIG. 2;

[0015]FIG. 6 is a fourth step of a control sequence of the circuit ofFIG. 2;

[0016]FIG. 7 is a top view of a first embodiment of a starter-generatorsystem;

[0017]FIG. 8 is a front view of a first embodiment of a tensioningsystem for the starter-generator system of FIG. 7;

[0018]FIG. 9 is a front view of second embodiment of a tensioning systemfor the starter-generator system of FIG. 7;

[0019]FIG. 10 is a front view of third embodiment of a tensioning systemfor the starter-generator system of FIG. 7;

[0020]FIG. 11 is a front view of fourth embodiment of a tensioningsystem for the starter-generator system of FIG. 7;

[0021]FIG. 12 is a top view of a second embodiment of astarter-generator system;

[0022]FIG. 13 is a view of a first embodiment of a tensioning system onthe starter-generator system of FIG. 12, taken along lines A-A;

[0023]FIG. 14 is a view of a second embodiment of a tensioning system onthe starter-generator system of FIG. 12, taken along lines A-A;

[0024]FIG. 15 is a top view of a third embodiment of a starter-generatorsystem; and

[0025]FIG. 16 is a view of a tensioning system for the starter-generatorsystem of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Starter-generators give rise to issues that affect the cost,complexity, and reliability of such systems. First, the drive mechanismconnected to a starter-generator handles power in two directions, whichpresents a unique tensioning problem for the drive mechanism. Second,there is a large gap between torque and speed requirements for startingan engine versus generating electricity. The differing torque and speedrequirements have typically been overcome by the use of transmissionhaving a different ratio for each the starting function and thegenerating function. Such transmissions typically required a gearbox anda switching clutch, which adds cost, complexity, and decreasedreliability of starter-generators.

[0027] Referring to the Figures and particularly to FIG. 1, a belt orchain drive mechanism 10 is shown handling power transmission in twodirections, and, thus illustrates the unique tensioning problem for thedrive mechanism. Drive mechanism 10 includes a first pulley or sprocket12, a second pulley or sprocket 14 and a chain or belt 16. In theinstance where first sprocket 12 is the drive sprocket driving mechanism10 in the direction of arrow 18, second sprocket 14 becomes the drivensprocket and first sprocket 12 acts on chain 16 such that the chain hasa tight-side or pulled-side 20 and a slack-side or pushed side 22.

[0028] Conversely, in the instance where second sprocket 14 is the drivesprocket driving mechanism 10 in the direction of arrow 24, firstsprocket 12 becomes the driven sprocket and second sprocket 14 acts onchain 16 such that the chain has a tight-side 26 and a slack-side 28. Ineither instance, a chain tensioner is needed on slack-side 22 and 28 tomaintain chain 16 operatively engaged with drive sprocket 12 and 14,respectively. Thus, where the drive sprocket and the driven sprocketchange place, the tight-side and slack-side of drive mechanism 10 alsochange place, giving rise to a need for more than one tensioner in thedrive mechanism. It should be noted that the belt or chain of drivemechanism 10 does not change its direction of rotation, rather only thesource of power (i.e., the drive sprocket) changes.

[0029] Embodiments of starter-generator system 100 are illustrated inFIGS. 7, 12 and 14. Generally, system 100 provides a starting functionto an internal combustion engine 110 and a generating function to abattery 140. System 100 includes a starter-generator 130 electricallycoupled to battery 140 by a lead 141. Starter-generator 130 isoperatively connected to engine 110 by a belt or chain drive mechanism10. Thus, starter-generator 130 performs dual functions of startingengine 110 and generating electrical output to battery 140. Belt orchain drive mechanism 10 is described in this application by way ofexample as either a belt drive mechanism or a chain drive mechanism,however both belt and chain drive mechanisms are considered within thescope of the present invention.

[0030] Starter-generator 130 is adapted to provide either anengine-cranking torque 200 to drive mechanism 10 or receive agenerator-cranking torque 300 from the drive mechanism. By way ofexample, operation of starter-generator 130 is described with respect toFIGS. 2 through 6. Starter-generator 130 is a three-phase rotary machineincluding a rectifier bridge 30 and a unit 32 for controlling therectifier bridge. Starter-generator 130 includes a coil-carrying rotor34 constituting the primary magnetic circuit associated with two ringsand with two brushes that convey excitation current (of the order of afew amps); and a stator 36 carrying a plurality of coils constitutingthe secondary magnetic circuit, connected in star or delta configurationin the common case of a three-phase structure and acting, duringgenerating operation, to deliver converted electrical power to therectifier bridge 30 (several tens of amps at a voltage of the same orderas the battery voltage).

[0031] Bridge 30 is connected to the various phases of the stator 36 andis connected between ground and a power supply terminal of a battery140. Bridge 30 includes a plurality of diodes 40 forming a rectifierbridge, and a plurality of switches 42, such as transistors. Switches 42are connected in parallel with respective diodes 40 and control thevarious phases (e.g., starting and generating) of starter-generator 130.

[0032] During a starting function, diodes 40 act as freewheel diodes,whereas in a generating function, the diodes act as a rectifier bridge.Switches 42 are advantageously MOSFET type transistors. Switches 42include a diode between drain and source. Consequently, the switches 42enable bridge 30 to be implemented using transistor components only thatthen act both as switches and as freewheel diodes.

[0033] The starting function of starter-generator 130 is achieved byimposing DC on the primary magnetic circuit rotor 34 and by deliveringsignals that are phase-shifted by 120 degrees to the phases of stator36, which signals are ideally sinewave signals, but may optionally besquarewave signals or trapezoidal wave signals. Referring now to FIGS. 3through 6, an example of a control sequence for switches 42 isillustrated. The sequence is made up of squarewave signals issued by thecontrol unit. The signals A, B, and C shown in these Figures are controlsignals for those of switches 42 in bridge 30 which are connected toground. The signals A′, B′, and C′ which control the other transistors,i.e. those connected to battery 140, are signals that are invertedrelative to the signals A, B, and C, without overlapping them. This isshown in FIG. 6 where the signal C′ is drawn for controlling thetransistor connected to the transistor controlled by the signal C. Withthis kind of control, the rotor performs one full revolution while eachof the phases goes through a number of periods equal to the number ofpairs of poles of the rotor (e.g. eight).

[0034] This starting operation is used for driving engine 110 to startit, thereby making it possible to eliminate the starter and theassociated drive ring, and also the power cabling generally associatedwith the starter. To enable engine 110 to be started in this way, thecontrol signals for switches 42 are advantageously variable frequencysignals, at a frequency that is regulated to be increasing by unit 32,so as to avoid any slip of the rotor relative to the rotating magneticfield created by the stator. For example, frequency regulation may beprovided by unit 32 in such a manner so as to guarantee that thealternator has a speed profile enabling the engine to be started.

[0035] Control unit 32 includes a means for recognizing a code signalthat authorizes engine starting. This signal is transmitted to the unit32 by a code transmitter means inside the vehicle. The unit 32 switcheson the transistors 42 in a manner suitable for starting the engine onlyif it receives the code signal. Consequently, the control unit 32 andthe code transmitter means which transmit the unlocking signal to saidunit, constitute a system for immobilizing the engine.

[0036] After engine 110 has started, unit 32 controls the transistors 42so as to operate in a generating mode. Unit 32 controls switches 42 sothat all of them are open circuit across the terminals of all of thediodes. The bridge 32 then reverts to being a rectifier bridge. Inanother possible embodiment, the transistors 42 are controlled so as toshort circuit the conductive diodes. They are caused to be open circuitonly across the terminals of non-conductive diodes. Thus, a current nolonger passes through the conductive diodes, such that the shortcircuits made in this way serve to reduce losses. To synchronize controlof transistors 42 relative to the switching from the conductive state tothe non-conductive state of diodes 40, unit 32 is connected to a meansfor detecting when diodes 40 pass from one state to another. By way ofexample, these means may be constituted by a sensor, such as a Halleffect sensor, for measuring the angular position of the rotor relativeto the stator. Such a sensor may also be used for determining the speedof the rotor, e.g. by counting pulses in a given time window, so as toenable the unit to detect that engine 110 has started and thus switchfrom operating in starting mode to operating in generating mode.

[0037] Also, means 44 are provided for regulating voltage so as tomaintain the voltage of battery 140 at a suitable level. Provision isalso made for a switch 46, e.g. another MOSFET type switch, whose ON orOFF state is controlled by the control unit. Switch 46 is designed toshort circuit the regulator in starting mode so that the secondarymagnetic circuit 36 is then directly excited by battery 140.

[0038] Thus when starter-generator 130 is in the starting mode,engine-cranking torque 200 is applied by drive mechanism 10 from thestarter-generator to engine 110. Moreover, when starter-generator 130 isin the generating mode, generator-cranking torque 300 is applied bydrive mechanism from engine 110 to the starter-generator. It should berecognized that the operation of starter-generator 130 has beendescribed above by way of example only and that other starter-generatorsadapted to provide a starting function to engine 110 and a generatingfunction to battery 140 are considered within the scope of the presentinvention.

[0039] Starter-generator 130 described above is adapted for use in theposition typically used for either automobile starters or alternators.Therefore, no complicated design changes to engine 110 are required forimplementation of starter-generator 130.

[0040] Referring now to FIG. 7, a tensioning system 100 is illustrated.System 100 includes engine 110, a starter-generator 130 electricallycoupled to battery 140 by a lead 141 and belt or chain drive mechanism10. Once started, engine 110 drives a flywheel 116 operatively connectedto a transmission 105 to propel the vehicle. Drive mechanism 10 has asingle belt 150 connected to engine 110, and starter-generator 130.

[0041] Engine 110 includes a crankshaft 112 having a crank pulley 114operatively connected thereto. Similarly, starter-generator 130 includesa starter-generator shaft 132 having a starter-generator pulley 134operatively connected thereto. Belt 150 is configured to frictionallyengage pulleys 114 and 134. In addition, and if necessary, belt 150 isconfigured to drive pulleys of other vehicle accessory systems,including but not limited to cooling systems, air conditioning systemsand power steering systems. For example, a pulley 124 is illustrated asdriving a water pump 120 of an engine cooling system. Of course, othersystems may or may not be driven by belt 150. At a minimum, system 100includes belt 150 and pulleys 114 and 134. Thus, as crank pulley 14 isdriven by engine 110, belt 150 rotates pulleys 114 and 134.

[0042] Upon activation by a user, starter-generator 130 draws energyfrom battery 140 through lead 141 to rotate starter-generator shaft 132.Shown in FIG. 8, starter-generator shaft 132 in turn rotatesstarter-generator pulley 134 to impart engine-cranking torque 200 tobelt 150. Thus, belt 150 being operatively connected to crank pulley 114drives crankshaft 112. Engine-cranking torque 200 acts on crankshaft 112to rotate engine 110 as required for engine starting procedures.

[0043] As shown in FIG. 8, during the starting of engine 110, belt 150has a tight-side 133 and a slack-side 135 created on either side ofstarter-generator pulley 134. A passive tensioning system 170 isprovided at slack-side 135 of belt 150 to remove the slack, keeping thebelt in operative engagement with starter-generator pulley 134. Passivetensioning system 170 includes an idler pulley 172 biased into operativeengagement with belt 150 so as to remove the slack from slack-side 135of the belt. Preferably, pulley 172 is biased into operative engagementwith belt 150 by a spring connection 174 mounted on engine 110 orelsewhere on the vehicle, such as, but not limited to the transmission,the exhaust manifold, or the vehicle body.

[0044] After engine 110 has been started, starter-generator 130generates an electrical output to battery 140 through lead 141. Shown inFIG. 9, engine 110 rotates crankshaft 112 and crankshaft pulley 114 toimpart a generator-cranking torque 300 to belt 150. Thus, belt 150 beingoperatively connected to starter-generator pulley 134 drivesstarter-generator shaft 132. Generator-cranking torque 300 acts onstarter-generator shaft 132 to rotate starter-generator 130, whichgenerates the electrical output to battery 140 through lead 141.Starter-generator 130 is described by way of example as receivingelectrical energy from and providing electrical energy to battery 140,however it is considered within the scope of the present invention forthe starter-generator to receive or provide electrical energy to or fromother devices. In one embodiment, generator-cranking torque 300 alsoacts to rotate pump pulley 124 of water pump 120 in order to provide aflow of cooling fluid to engine 110 as required in engine coolingsystems.

[0045] During the generation of the electrical output to battery bystarter-generator 130 shown in FIG. 9, belt 150 has a tight-side 113 anda slack-side 115 on either side of crankshaft pulley 114. Passivetensioning system 170 is also provided at slack-side 115 of belt 150 toremove the slack, keeping the belt in operative engagement withcrankshaft pulley 114. Idler pulley 172 is biased into operativeengagement with belt 150 so as to remove the slack from slack-side 115of belt 150. Preferably, pulley 172 is biased into operative engagementwith belt 150 by spring connection 174 mounted on engine 110 orelsewhere on the vehicle, such as, but not limited to the transmission,the exhaust manifold, or the vehicle body.

[0046] Accordingly, tensioning system 170 maintains belt 150 inengagement with pulleys 114 and 134 during the charging and startingoperations, respectively. It has been determined that drive mechanism 10having tensioning system 170 only on the slack-side of the pulley 114 or134 generating the greater torque is sufficient for proper operation ofstarter-generator 130. More specifically, passive tensioning system 170is placed at slack side 115 when generator-cranking torque 300 isgreater than engine-cranking torque 200 as shown in FIG. 9. Alternately,passive tensioning system 170 is placed at slack-side 135 whenengine-cranking torque 200 is greater than generator-cranking torque300, as shown in FIG. 8.

[0047] For example, if engine-cranking torque 200 is greater thangenerator-cranking torque 300 (e.g., engine 110 is started at very coldambient temperatures when oil in the engine is very viscous), thentensioning system 170 is provided only at slack-side 135. Oppositely, ifengine-cranking torque 200 is lower than generator-cranking torque 300(e.g., high electrical load on battery 140), then tensioning system 170is provided only at slack-side 115. The life of belt 150 is typicallyinversely proportional to its maximum tension. Thus, placing passivetensioning system 170 only on one of slacksides 115 and 135 increasesthe service life of belt 150.

[0048] An alternate embodiment of the tensioning system is illustratedin FIG. 10. Here, component parts performing similar or analogousfunctions are numbered in multiples of one hundred. In this embodiment,an active tensioning system 270 is provided for starter-generator pulley134 and an active tensioning system 370 is provided for crank pulley114. Active tensioning systems 270 and 370 actively or automaticallyengage drive mechanism 10 as needed. In this embodiment, activetensioning system 270 includes an idler pulley 272, a spring connection274, and a solenoid 276. Spring connection 274 is mounted on engine 110or elsewhere on the vehicle, such as, but not limited to thetransmission, the exhaust manifold, or the vehicle body. Solenoid 276 isadapted to extend idler pulley 272 into operative engagement withslack-side 135, and spring connection 274 is adapted to retract theidler pulley upon deactivation of the solenoid. Similarly, activetensioning system 370 includes an idler pulley 372, a spring connection374 and a solenoid 376. Spring connection 374 is mounted on engine 110or elsewhere on the vehicle, such as, but not limited to thetransmission, the exhaust manifold, or the vehicle body. Solenoid 376 isadapted to extend idler pulley 372 into operative engagement withslack-side 115, and spring connection 374 is adapted to retract theidler pulley upon deactivation of the solenoid.

[0049] Thus, during starting when engine-cranking torque 200 is impartedto belt 150 to create slack-side 135 and tight-side 133 (shown in FIG.10 in dotted lines), solenoid 276 of active tensioning system 270 isactivated to extend idler pulley 272 into operative engagement with theslack-side. After engine 110 has been started and engine-cranking torque200 is removed from belt 150, solenoid 276 of active tensioning system270 is deactivated such that spring connection 274 retracts idler pulley272 out of operative engagement with slack-side 135.

[0050] Similarly, during generation of energy when generator-crankingtorque 300 is imparted to belt 150 to create slack-side 115 andtight-side 113 (shown in FIG. 10 in solid lines), solenoid 376 of activetensioning system 370 is activated to extend idler pulley 372 intooperative engagement with the slack-side. After battery 140 has beencharged and generator-cranking torque 300 is removed from belt 150,solenoid 376 of active tensioning system 370 is deactivated such thatspring connection 374 retracts idler pulley 372 out of operativeengagement with slack-side 115.

[0051] The selective extension and retraction of active tensioningsystems 270 and 370 increases the service life in belt 150 since, asdiscussed above, the life of the belt 150 is inversely proportional toits maximum tension.

[0052] Another embodiment of the tensioning system is provided in FIG.11. In this embodiment, passive tensioning system 470 is provided forcrank pulley 114 and active tensioning system 570 is provided forstarter-generator pulley 134. Active tensioning system 570 includes anidler pulley 572, a spring connection 574, and solenoid 576. Springconnection 574 is mounted on engine 110 or elsewhere on the vehicle,such as, but not limited to the transmission, the exhaust manifold, orthe vehicle body. Solenoid 576 is adapted to extend idler pulley 572into operative engagement with slack-side 135, and spring connection 574is adapted to retract the idler pulley upon deactivation of thesolenoid. Passive tensioning system 470 includes idler pulley 472 andspring connection 474 mounted on engine 110 or elsewhere on the vehicle,such as, but not limited to the transmission, the exhaust manifold, orthe vehicle body. Spring connection 474 biases idler pulley 472 intooperative engagement with slack-side 115. In this embodiment, springconnection 474 of passive tensioning system 470 biases idler pulley 472into operative engagement with slack side 115 regardless of the state ofgenerator-cranking torque 300.

[0053] Thus, during starting when engine-cranking torque 200 is impartedto belt 150 to create slack-side 135 and tight-side 133 (shown in FIG.11 in dotted lines), solenoid 576 of active tensioning system 570 isactivated to extend idler pulley 572 into operative engagement with theslack-side. After engine 110 has been started and engine-cranking torque200 is removed from belt 150, solenoid 576 of active tensioning system570 is deactivated such that spring connection 574 retracts idler pulley572 out of operative engagement with slack-side 135.

[0054] The selective extension and retraction of tensioning system 570increases the service life in belt 150 since, as discussed above, thelife of the belt is typically inversely proportional to its maximumtension. The inclusion of one active tensioning system 570 and onepassive tensioning system 470 decreases complexity and cost. Activetensioning system 570 has a low power/energy requirement since solenoid576 is activated for only used for a very short time, namely duringengine cranking.

[0055] Active tensioning systems 270, 370, and 570 are described aboveby way of example as including solenoids 276, 376, and 576 and springconnections 274, 374, and 574. However, alternate devices for extendingand retracting idler pulley 272, 372, and 574 are considered within thescope of the present invention. For example, alternate embodimentsinclude, but are not limited to, extension and retraction by anactuator, or a lever.

[0056] An alternate embodiment of starter-generator system 100 isillustrated in FIGS. 12 through 14. System 100 includes engine 110, astarter generator 130 electrically coupled to battery 140 by a lead 141and belt or chain drive mechanism 10, namely a chain 160. Once started,engine 110 drives a flywheel 116 operatively connected to a transmission105 to propel the vehicle and drives a crankshaft 112 having a crankpulley 114 operatively connected thereto.

[0057] Cooling system 120 includes a pump-shaft 122 having a pump pulley124 operatively connected thereto and starter-generator 130 includes astarter-generator shaft 132 having a starter-generator sprocket 134operatively connected thereto. Accessory belt 150 operatively connectscrank pulley 114 and pump pulley 124. A chain 160 operatively connectsstarter-generator sprocket 134 and flywheel 116.

[0058] Upon activation by a user, starter-generator 130 draws energyfrom battery 140 through lead 141 to rotate starter-generator shaft 132.Shown in FIG. 13 in dotted lines, starter-generator shaft 132 in turnrotates starter-generator sprocket 134 to impart an engine-crankingtorque 200 to chain 160. Thus, engine-cranking torque 200 acts onflywheel 116 to rotate engine 110 as required for engine startingprocedures. During the starting of engine 110, chain 160 has atight-side 133 and a slack-side 135 on either side of starter-generatorsprocket 134. A tensioning system 180 is provided at slack-side 135 ofchain 160 to remove the slack, keeping the chain in operative engagementwith starter-generator sprocket 134.

[0059] After engine 110 has been started, starter-generator 130generates an electrical output to battery 140 through lead 141. Engine110, when running, rotates flywheel 116 and crankshaft pulley 114. Belt150 being operatively connected to crankshaft pulley 114 and coolingsystem pulley 124, acts to rotate pump-shaft 122 to drive cooling system120 in order to provide cooling to engine 110. Simultaneously, flywheel116 imparts a generator-cranking torque 300 to chain 160.

[0060] Generator-cranking torque 300 acts on starter-generator shaft 132to rotate starter-generator 130, which generates the electrical outputto battery 140 through lead 141. During the generation of the electricaloutput to battery 140 by starter-generator 130, chain 160 has atight-side 117 and a slack-side 118 on either side of flywheel 116,shown in FIG. 13 in solid lines. Tensioning system 180 is also providedat slack-side 118 of chain 160 to remove the slack, keeping the chain inoperative engagement with flywheel 116.

[0061] Tensioning system 180 is an active tensioning system, namely itactively or automatically tensions chain 160 as needed. Tensioningsystem 180 includes a guide 182, a first idler sprocket 184, a secondidler sprocket 186, and a spring 188. Guide 182, preferably a shaft, ismounted on engine 110 or elsewhere on the vehicle, such as, but notlimited to the transmission, the exhaust manifold, or the vehicle body.First idler sprocket 184 is adapted to slide or float up and down onguide 182. Similarly, second idler sprocket 186 is adapted to slide orfloat up and down on guide 182. First idler sprocket 184 and secondidler sprocket 186 are tied together by spring 188 such that the springbiases the sprockets 184, 186 towards one another. Thus, the assembly offirst idler sprocket 184, second idler sprocket 186, and spring 188 arepermitted to slide together on guide 182.

[0062] During starting, shown in FIG. 13 in dotted lines, the tension intight-side 133 of chain 160 acts on second idler sprocket 186 to slidetensioning system 180 downwards until first idler sprocket 184 takes upthe slack in slack-side 135. Thus, tensioning system 180 being in itslower position and being biased by spring 188 takes up the slack inchain 160. During generating, shown in solid lines, the tension intight-side 117 of chain 160 acts on first idler sprocket 184 to slidetensioning system 180 upwards until second idler sprocket 186 takes upthe slack in slack-side 135. Thus, tensioning system 180 being in itsupper position and being biased by spring 188 takes up the stack inchain 160.

[0063] Friction between guide 182 and sprockets 184, 186 acts to dampenvibrations induced by chain 160 traveling. Alternately, an active meansof damping (not shown) such as, but not limited to a hydraulic damperattached between guide 182 and sprockets 184, 186 and/or spring 188 isused to further dampen vibrations induced by traveling of chain 160.

[0064] Referring now to FIG. 14, a tensioning system 280 is illustrated.During the generation of the electrical output to battery 140 bystarter-generator 130, chain 160 has a tight-side 117 and a slack-side118 on either side of flywheel 116. During starting, chain 160 has atight-side 133 and a slack-side 135 on either side of starter-generatorpulley 134.

[0065] Tensioning system 280 is a constant tensioning system, namely itprovides tension to chain 160 during starting, generating and staticconditions. Tensioning system 280 includes a first or upper tensioningmechanism 282 and a second or lower tensioning mechanism 284. Uppertensioning mechanism 282 biases a low-friction chain guide 286 intooperative engagement with chain 160 by a spring connection 288 mountedon engine 110 or elsewhere on the vehicle, such as, but not limited tothe transmission, the exhaust manifold, or the vehicle body.

[0066] Lower tensioning mechanism 284 includes an idler sprocket 290 inoperative engagement with chain 160. Sprocket 290 is rotatably mountedby a bracket 292 to engine 110 or elsewhere on the vehicle, such as, butnot limited to the transmission, the exhaust manifold, or the vehiclebody. Bracket 292 is adapted to mount idler sprocket 290 in operativeengagement with chain 160. For example, bracket 292 includes a take-upsystem, such as but not limited to a screw 294 and a slot 296.Accordingly, lower tensioning mechanism 284 removes any initial slackfrom belt 160 in a normal or static state.

[0067] During starting or the application of starting torque 200, springconnection 288 of upper tensioning mechanism 282 biases low-frictionchain guide 286 towards chain 160 to remove slack from slack-side 135.During generating or the application of generating torque 300, idlersprocket 290 continues to tension slack from slack-side 118 of chain160, while low-friction chain guide 286 of upper tensioning mechanism282 applies a very low drag force on the chain. Accordingly, duringgenerating upper tensioning mechanism 282 does not affect theperformance of chain drive mechanism 10 since the upper tensioningmechanism is not adding additional load to the chain.

[0068] Yet another embodiment of starter-generator system 100 isprovided in FIGS. 15 and 16. System 100 includes engine 110, astarter-generator 130 electrically coupled to battery 140 by a lead 141and belt or chain drive mechanism 10, namely a belt 190. Once started,engine 110 drives a flywheel 116 operatively connected to a transmission105 to propel the vehicle. Engine 110 includes a crankshaft 112 havingan accessory pulley 108 and a crank pulley 114 operatively connectedthereto.

[0069] Cooling system 120 includes a pump-shaft 122 having a pump pulley124 operatively connected thereto and starter-generator 130 includes astarter-generator shaft 132 having a starter-generator pulley 134operatively connected thereto. Accessory belt 150 operatively connectsaccessory pulley 108 and pump pulley 124. Belt 190 operatively connectsstarter-generator pulley 134 and crank pulley 114.

[0070] Upon activation by a user, starter-generator 130 draws energyfrom battery 140 through lead 141 to rotate starter-generator shaft 132.Shown in FIG. 16 in dotted lines, starter-generator shaft 132 in turnrotates starter-generator pulley 134 to impart an engine-cranking torque200 to starter-generator belt 190. Thus, engine-cranking torque 200 actson crank pulley 114 to rotate engine 110 as required for engine startingprocedures. During the starting of engine 110, starter-generator belt190 has a tight-side 133 and a slack-side 135 on either side ofstarter-generator pulley 134. Tensioning system 180 is provided atslack-side 135 of belt 190 to remove the slack, keeping the belt inoperative engagement with starter-generator pulley 134.

[0071] After engine 110 has been started, starter-generator 130generates an electrical output to battery 140 through lead 141. Engine110, when running, rotates and crank pulley 114. Accessory belt 150being operatively connected to accessory pulley 108 and cooling systempulley 124, acts to rotate pump-shaft 122 to drive cooling system 120 inorder to provide cooling to engine 110. Simultaneously, crank pulley 114imparts a generator-cranking torque 300 to belt 190.

[0072] Generator-cranking torque 300 acts on starter-generator shaft 132to rotate starter-generator 130, which generates the electrical outputto battery 140 through lead 141. During the generation of the electricaloutput to battery 140 by starter-generator 130, belt 190 has atight-side 117 and a slack-side 118 on either side of crank pulley 114,as shown in FIG. 16 in solid lines. Tensioning system 180 is alsoprovided at slack-side 118 of belt 190 to remove the slack, keeping thebelt in operative engagement with crank pulley 114.

[0073] Tensioning system 180 shown in FIG. 16, similar to the discussionabove with respect to FIG. 13, is an active tensioning system thatactively or automatically engages belt 190 as needed. Tensioning system180 includes guide 182, first idler pulley 184, second idler pulley 186,and spring 188. Guide 182, preferably a shaft, is mounted on engine 110or elsewhere on the vehicle, such as, but not limited to thetransmission, the exhaust manifold, or the vehicle body. First idlerpulley 184 is adapted to slide or float up and down on guide 182.Similarly, second idler pulley 186 is adapted to slide or float up anddown on guide 182. First idler pulley 184 and second idler pulley 186are tied together by spring 188 such that the spring biases the pulley184, 186 towards one another. Thus, the assembly of first idler pulley184, second idler pulley 186, and spring 188 are permitted to slidetogether on guide 182.

[0074] During starting, shown in FIG. 16 in dotted lines, the tension intight-side 133 of belt 190 acts on second idler pulley 186 b slidetensioning system 180 downwards until first idler pulley 184 takes upthe slack in slack-side 135. Thus, tensioning system 180 being in itslower position and being biased by spring 188 takes up the slack in belt190. During generating, shown in solid lines, the tension in tight-side117 of belt 190 acts on first idler pulley 184 to slide tensioningsystem 180 upwards until second idler pulley 186 takes up the slack inslack-side 118. Thus, tensioning system 180 being in its upper positionand being biased by spring 188 takes up the slack in belt 190.

[0075] For purposes of clarity, tensioning system 180 has been describedby way of example as part of a two pulley/sprocket system. However, itis considered within the scope of the present invention for use of suchtensioning systems 180 with pulley/sprocket systems having more than twopulleys.

[0076] A difference between torque and speed requirements for startingan engine versus generating electricity exists. The tensioning systemsdescribed herein ensure that the belt/chain remains operativelyconnected to its respective pulleys/sprockets. Thus, it has beendetermined that the effect of the torque difference on starter-generator130 is minimized by adjusting the gear ratio of starter-generator pulley134 with respect to crank pulley 114 (or flywheel 116).

[0077] Engine-cranking torque 200, namely the torque supplied tocrankshaft 112, is equal to the torque provided by starter-generator 130multiplied by the gear ratio of the starter-generator pulley 134 withrespect to the crank pulley 114. The gear ratio should desirably bebetween 2:1 and 3:1. For example, if the gear ratio is 3:1 and engine110 requires 150 foot-pounds of torque for starting purposes,starter-generator 130 must generate 50 foot-pounds (ignoring losses) toprovide the required 150 foot-pounds at crankshaft 112.

[0078] Additionally, the electrical energy generated bystarter-generator 130 is proportional to the speed of crankshaft 112.Thus, at higher crankshaft 112 speeds more electrical energy isgenerated, and, conversely, at lower crankshaft speeds less electricalenergy is generated. Thus, in the example provided above where the gearratio is 3:1, if crankshaft 112 has a speed of 1000 rpm,starter-generator shaft 132 has a resulting speed of 3000 rpm.

[0079] Setting the gear ratio at higher than the desired range ofbetween 2:1 and 3:1, would decrease the amount of torquestarter-generator 130 must generate to provide the requiredengine-cranking torque 200. For example, if the gear ratio is 10:1 andengine 110 requires 150 foot-pounds of torque for starting purposes,starter-generator 130 must generate only 15 foot-pounds (ignoringlosses) to provide the required 150 foot-pounds at crankshaft 112.Moreover, in this example, if crankshaft 112 has a speed of 1000 rpm,starter-generator shaft 132 has a resulting speed of 10,000 rpm. Thus,when the ratio is set such that starter-generator 130 is required toproduce low amounts of torque, the resulting speed of starter-generatorshaft 132 tends to exceed the maximum rate determined from mechanicaland/or electrical restrictions in high velocity revolution. However, ithas been found that the desired ratio of between 2:1 and 3:1 balancesthe speed of starter-generator shaft 132 and the amount of torquestarter-generator 130 must generate.

[0080] Thus, starter-generator system 100 provides a low cost method forachieving a starter-generator. Drive mechanism 10 includes simple activeand passive tensioning systems. Moreover, starter-generator system 100eliminates the need for gearboxes and their switching clutches tocompensate for torque and speed differences during starting andgenerating.

[0081] While the invention has been described with reference to anexemplary embodiment, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An apparatus for starting an engine, comprising: a starter generatorbeing configured to provide a rotational starting torque to a first sideof a drive mechanism and receive a rotational generating torque from asecond side of said drive mechanism, said starter generator generating acurrent when said drive mechanism receives said rotational generatingtorque, said drive mechanism being configured, dimensioned andpositioned to engage said starter generator and a crankshaft of saidengine, said rotational generating torque or said rotational startingtorque being a greater torque; and a passive tensioning system incooperation with said drive mechanism to tension said drive mechanism atonly said first side or said second side, respectively, having saidgreater torque.
 2. The apparatus as in claim 1, wherein said rotationalgenerating torque is said greater torque and said passive tensioningsystem cooperates with said drive mechanism at said second side.
 3. Thestarter-generator system as in claim 1, wherein said rotational startingtorque is said greater torque and said passive tensioning systemcooperates with said drive mechanism at said first side.
 4. Thestarter-generator system as in claim 1, wherein said passive tensioningsystem comprises an idler pulley biased into operative engagement withsaid drive mechanism.
 5. The starter-generator system as in claim 4,wherein said idler pulley is biased into operative engagement with saiddrive mechanism by a spring connection mounted on a structure.
 6. Thestarter-generator system of claim 1, wherein said drive mechanismcompensates for differences in said rotational generating torque andsaid rotational starting torque with a non-adjusting gear ratio in arange between 2:1 to 3:1.
 7. The starter-generator system of claim 1,wherein said drive mechanism is selected from the group consisting of abelt driven system and a chain driven system.
 8. The starter-generatorsystem of claim 1, wherein said drive mechanism connects a pulley ofsaid starter-generator and said crankshaft of said internal combustionengine at either a crankshaft pulley of said internal combustion engineor a flywheel of said internal combustion engine.
 9. An apparatus forstarting an internal combustion engine, comprising: a starter-generatorbeing operable in a first direction for generating a current and asecond direction for starting said internal combustion engine; a drivemechanism connecting said starter-generator and said internal combustionengine by a non-adjusting gear ratio in a range between 2:1 to 3:1, saidstarter-generator operates in said first direction to generate saidcurrent by receiving a charging torque from said internal combustionengine imparted to a first side of said drive mechanism and saidstarter-generator operates in said second direction to start saidinternal combustion engine by imparting a starting torque to a secondside of said drive mechanism; a first tensioning system cooperating withsaid drive mechanism to tension said drive mechanism at said first sideduring application of said charging torque; and a second tensioningsystem cooperating with said drive mechanism to tension said drivemechanism at said second side during application of said startingtorque.
 10. The apparatus of claim 9, wherein said drive mechanismconnects said starter-generator and said internal combustion engine ateither a crankshaft of said internal combustion engine or a flywheel ofsaid internal combustion engine.
 11. The apparatus of claim 9, whereinsaid drive mechanism is selected from the group consisting of a beltdriven system and a chain driven system.
 12. The apparatus of claim 9,wherein said first tensioning system is a passive tensioning system andsaid second tensioning system is an active tensioning system.
 13. Theapparatus of claim 12, wherein said passive tensioning system comprisesan idler pulley biased into operative engagement with said drivemechanism.
 14. The apparatus of claim 13, wherein said idler pulley isbiased into operative engagement with said drive mechanism by a springconnection mounted on a structure.
 15. The apparatus of claim 12,wherein said active tensioning system comprises an idler pulleyextendable into operative engagement with said drive mechanism duringapplication of said starting torque and retractable out of operativeengagement with said drive mechanism after removal of said startingtorque.
 16. The apparatus of claim 15, further comprising a solenoid forextending said idler pulley and a biasing member for retracting saididler pulley.
 17. The apparatus of claim 16, wherein said firsttensioning system is a first active tensioning system and said secondtensioning system is a second active tensioning system.
 18. Theapparatus of claim 17, wherein said first active tensioning systemcomprises a first idler pulley extendable into operative engagement withsaid drive mechanism during application of said starting torque andretractable out of operative engagement with said drive mechanism afterremoval of said charging torque, and said second active tensioningsystem comprises a second idler pulley extendable into operativeengagement with said drive mechanism during application of said startingtorque and retractable out of operative engagement with said drivemechanism after removal of said starting torque.
 19. The apparatus ofclaim 18, further comprising a first solenoid for extending said firstidler pulley, a first biasing member for retracting said first idlerpulley, a second solenoid for extending said second idler pulley and asecond biasing member for retracting said second idler pulley.
 20. Anactive tensioning system, comprising: a drive mechanism operable tocreate a first slack side and a first tight side of said drive mechanismand operable to create a second slack side and a second tight side ofsaid drive mechanism, said first slack side and said second tight sidebeing coincident, said second slack side and said first tight side beingcoincident; a guide mountable on a structure; a first idler sprocketbeing operatively coupled with said first slack side of said drivemechanism and being slidable on said guide; a second idler sprocketbeing operatively coupled with said second slack side of said drivemechanism and being slidable on said guide; and a biasing memberconnecting said first idler sprocket and said second idler sprocket andbiasing said first idler sprocket and said second idler sprocket towardsone another such that upon creation of said first slack side and saidfirst tight side, said first tight side acts upon said second idlersprocket to slide said first idler sprocket and said second idlersprocket upon said guide to tension said drive mechanism, and such thatupon creation of said second slack side and said second tight side, saidsecond tight side acts upon said first idler sprocket to slide saidfirst idler sprocket and said second idler sprocket upon said guide totension said drive mechanism.
 21. The active tensioning system of claim20, wherein said drive mechanism is selected from the group consistingof a belt driven system and a chain driven system.
 22. Astarter-generator system for use in a vehicle, comprising: astarter-generator being adapted to operate in a charging mode and astarting mode; a drive mechanism connecting said starter-generator andan internal combustion engine, said starter-generator operates in acharging mode by receiving a charging torque from a first side of saiddrive mechanism and operates in said starting mode by imparting astarting torque to a second side of said drive mechanism, said drivemechanism compensating for differences in said charging torque and saidstarting torque with a non-adjusting gear ratio in a range between 2:1to 3:1; and an active tensioning system cooperating with said drivemechanism to tension said drive mechanism at said first side duringapplication of said charging torque or at said second side duringapplication of said starting torque.
 23. The starter-generator system ofclaim 22, wherein said drive mechanism comprises: a guide mountable on astructure; a first idler sprocket being operatively coupled with saidfirst side of said drive mechanism and being slidable on said guide; asecond idler sprocket being operatively coupled with said second side ofsaid drive mechanism and being slidable on said guide; and a biasingmember connecting said first idler sprocket and said second idlersprocket and biasing said first idler sprocket and said second idlersprocket towards one another such that during application of saidcharging torque said second side acts upon said second idler sprocket toslide said first idler sprocket and said second idler sprocket upon saidguide to tension said drive mechanism, and such that upon creation ofsaid starting torque said first side acts upon said first idler sprocketto slide said first idler sprocket and said second idler sprocket uponsaid guide to tension said drive mechanism.
 24. The starter-generatorsystem of claim 22, wherein said drive mechanism is selected from thegroup consisting of a belt driven system and a chain driven system. 25.The starter-generator system of claim 22, wherein said drive mechanismconnects said starter-generator and said internal combustion engine ateither a crankshaft of said internal combustion engine or a flywheel ofsaid internal combustion engine.
 26. An apparatus for starting aninternal combustion engine, comprising: a starter-generator beingoperable in a first direction for generating a current and a seconddirection for starting said internal combustion engine; a drivemechanism connecting said starter-generator and said internal combustionengine by a non-adjusting gear ratio in a range between 2:1 to 3:1, saidstarter-generator operates in said first direction to generate saidcurrent by receiving a charging torque from said internal combustionengine imparted to a first side of said drive mechanism and saidstarter-generator operates in said second direction to start saidinternal combustion engine by imparting a starting torque to a secondside of said drive mechanism; a constant tensioning system having afirst tensioning mechanism and a second tensioning mechanism, said firsttensioning mechanism system cooperating with said drive mechanism totension said drive mechanism at said first side, and said secondtensioning mechanism cooperating with said drive mechanism to tensionsaid drive mechanism at said second side.
 27. The apparatus of claim 26,wherein said first tensioning mechanism includes a low-friction chainguide biased into operative engagement with said chain and said secondtensioning mechanism includes an idler sprocket into operativeengagement with said drive mechanism.